For Cobra, Mongoose, Rx SE's. I have maybe a handful of shaves on the first two razors and don't recall the blades I used, but the shaves were harsh. I'm looking forward to trying the Rx one day but need a bit of a primer on what the SE blade pool has to offer. I have a sampler pack of these:

If the first shave to three are rough from a SE shave then I highly suggest palm stropping the blade to smooth them out.

Kai Milds couldn't cut my stubble.
Feather Pros are the perfect blend of sharp & smooth for me
Feather Supers are just too wild for me & simply not necessary given how well the regular Pros work for me.

I too am trying to find a nice match for my single edge razors...I only have had a handful of shaves myself since acquiring my mongoose and king cobra. I have only used Kai blades up until this point. I have managed some quality shaves. However, with that said there is quite a bit of tug from these blades. I am interested in stepping up to some feather Pros.

I like the Feather Pros the best but since I got the AlumiGoose which I feel is a little more aggressive than the stainless steel model, I have been experimenting with the Feather Pro Guard blades. Only one shave with the Pro Guard so far so too soon to tell.

The Feather Professional blades are perfect in my Cobras but were too rough for me in the Mongoose. The ProGuard blades worked in every version of the Mongoose that I tried and the Supers resulted in excessive blood loss when used in either razor.
It may take a bit of experimenting to find the perfect blade for you.

I've tried many and now the only 2 blades that work into my SE rotation is the Feather Pro and Pro Super. I'm not sure what changed but I recently got the King Cobra with a Feather Pro dialed in and I'M NOW GETTING THE SMOOTHEST/CLOSEST SHAVE OF ANY DE RAZOR/BLADE COMBO I OWN.....INCLUDING MY WOLFMAN. I own both the King and Classic and pre-ordered the ATT SE....now seriously considering I might cancel my pre-order....why mess with a good thing

This might sound silly, but this change with the King Cobra actually occurred when I replaced the KC handle with a heavier/thicker handle...not sure if this resulted in a change in the angle or grip pressure or both....all I know is it's working like a charm.